The present invention relates generally to an apparatus for suppressing noise which radiates from the ignition system of an internal combustion engine, and more particularly relates to an apparatus for suppressing noise which generates from the distributor located in the ignition system.
The igniter in which an electric current has to be intermitted quickly in order to generate a spark discharge, radiates the noise which accompanies the occurrence of the spark discharge. It is well known that the noise disturbs radio broadcasting service, television broadcasting service and other kinds of radio communication systems and, as a result, the noise deteriorates the signal-to-noise ratio of each of the above-mentioned services and systems. Further, it is very important to know that the noise may also cause operational errors in electronic control circuits, mounted in vehicles, such as E.F.I. (electronic controlled fuel injection system), E.S.C. (electronic controlled skid control system) or E.A.T. (electronic controlled automatic transmission system), and, as a result, traffic safety may be threatened. On the other hand, the tendency for an electric current, flowing in the igniter to become very strong and to be intermitted very quickly in order to generate a strong spark discharge, becomes a common concept because of the increasing emphasis on clean exhaust gas. However, strong spark discharge is accompanied by extremely strong noise which aggravates the previously mentioned disturbance and operational errors.
For the purpose of suppressing the noise, various kinds of apparatuses or devices have been proposed. A first prior art example is provided by the Japanese Patent Publication No. 48-12012. In the first prior art example, the spark gap, between the electrodes of the distributor rotor and the stationary terminal in the distributor, is selected to be between 1.524 mm and 6.35 mm, which is wider than the spark gap used in the typical distributor. A second prior art example is provided by the Japanese Patent Publication No. 51-38853. In the second prior art example, an electrically high resistive layer is formed on each of the surfaces of the electrodes of the distributor rotor and/or the stationary terminals. A third prior art example is provided by the Japanese Patent Publication No. 52-15736. In the third prior art example, an electrically resistive member is inserted in the spark gap formed between the distributor rotor and the stationary terminal, and the spark discharge occurs between the distributor rotor and the stationary terminal, through said electrically resistive member. A fourth prior art example is provided by the Japanese Patent Publication No. 52-15737. In the fourth prior art example, a dielectric member is inserted in the spark gap formed between the distributor rotor and the stationary terminal, and the spark discharge occurs between the distributor rotor and the stationary terminal by way of the surface of said dielectric member.
Thus, the distributor, which incorporates either one of the above-mentioned first through fourth prior art examples, can exhibit remarkable suppression of the noise, when compared to the conventional distributor which contains no apparatus for suppressing the noise. Thereafter, the inventors have advanced further development on the apparatus for suppressing the noise, and finally succeeded in realizing the apparatus which is superior to any one of said prior art examples in suppressing the noise of the distributor. The developed distributor is characterised in that the distributor is comprised of a rotor and a plurality of stationary terminals, wherein a hollow insulating member is introduced into a discharging air gap formed between a discharging electrode of the rotor and each of the discharging electrodes of the stationary terminals, and thereby, a spark discharge, occurring between the discharging electrodes of the rotor and each said stationary terminal, is generated via through hole formed inside the hollow insulating member.
However, in the developed distributor having the hollow insulating member, improvement on a so-called advance angle has not yet been fully examined, which improvement resides in the fact that it should actually be very easy for the spark discharge to follow within a wide range of a variation of the advance angle by which the ignition timing of each spark plug is defined. In achieving such improvement, it must be taken into consideration that the hollow insulating member must be easily manufactured and also be low in cost. At the same time, on the other hand, the capability for igniting the fuel air mixture must not be weakened due to the presence of the hollow insulating member.